An image-reading device installed in a copy machine or a similar machine generally is made so that a carriage with a mirror is moved along an original document placed on a platen glass, image light of the original document is reflected by the mirror, and the reflected image light is guided to a light receiving device such as a CCD via a rod lens array (an arrangement of multiple gradient index lenses, known as SELFOC lenses), as disclosed in Japanese Laid-Open Patent Application H10-257251.
In addition, the image-reading device may be constructed so as to enable reading an image by moving an original document. With this type of image-reading device, a feeder for feeding the original to a position at one end of the platen glass is provided, the image is read while moving the original document, and the carriage is stopped at an end position. With this type of image-reading device, it is desirable that the platen glass be separated from the feeder in order to be isolated from vibrations associated with feeding the original document. Therefore, a separate end glass, known as a CVT glass in order to distinguish it from the platen glass, is used at the bottom of the feeder.
Additionally, the applicant of the present application has developed an image-reading device that does not require a mirror by providing a rod lens array (formed of SELFOC lenses) and a CCD on the carriage as an alternative to the mirror scan method described above. With this image-reading device, the optical axis of the rod lens array faces the vertical direction toward the platen glass, and the light that passes through the rod lens array directly forms an image at the CCD light receiving device.
However, since the focal depth of the rod lens array is narrower (0.5 mm or less being common) than lenses normally used in lens barrels, the distance between the rod lens array and the platen glass must be established very strictly in an image-reading device using a rod lens array as described above. In order to maintain a fixed distance between the original document and the carriage in this type of image-reading device, sliding members that protrude in the vertical direction are installed on the carriage, and the carriage, including these sliding members, is biased elastically upward so that the sliding members make contact with the bottom surface of the platen glass.
However, with the image-reading device described above, when the carriage moves between the platen glass and the CVT glass, resistance occurs as the sliding member passes across the gap between the two glasses. Due to this, there is the risk of the sliding member wearing rapidly and vibration occurring that results in the carriage not being at its appropriate height and the movement of the carriage not being properly synchronized with a driving motor, such as a stepping motor.